Method of blasting



Patented Feb. 26, 1935 UNITED STATES PATENT OFFICE 1,992,21e METHOD OF BLASTING William E. Kirst, Woodbury, N.-J., John w.

McCoy, Wllmingto DeL, and Clifford A.

Woodlr'ry. Media, Pa., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application March 1'1, 1932,

19 Claims.

Our invention relates to an improved method .of blasting ill which a relatively insensitive explosive is'utilized as the-main charge in combination with a priming charge comprising a more sensitive explosive. The invention relates more particularly to such an assembly in which the main charge comprisesan explosive of regulated sensitiveness.

In blasting work in hard rock the use of deto-' satisfaction in so far as their explosive execution is concerned. Some unavoidable disadvantages have, however, been connected with their use. These explosives are not only sensitive to shock and friction but are distinctly inflammable and a reasonable amount of care must therefore be exercised in their handling and transportation; Furthermore, they are relatively expensive due primarily to the use of a high percentage-cf a costly sensitizer and also to the .extra care required in their manufacture and transportation. It has heretofore been considered necessary in order that no misfires should occur in practical blasting, to employ explosives readily detonated by the blasting caps in common use. This is due to the fact that such failures bring hazards in removing the unexploded charge as well as undesirable expenditures for labor. -It is apparent, therefore, that the less sensitive explosives can be and yet be satisfactory for use, the greater and more numerous are the resulting advantages.

The use of insensitive explosives would be particularly desirable in quarry blasting where the amount of explosive used for a single blast is very large, often ranging from 10,000 to 30,000 lbs. When blasting on this scale the number of men involved in the operations of handling and loading explosives is considerable and all of these men are of necessity exposed to greater hazards when using sensitive explosives. Furthermore,' the most common method of blasting now used in quarries, and known as the well drill method, employs drill holes which range from 4 to 8 inches 1 A further attempt to make a in diameter and are often from 60 to 200 feet deep. The danger connected with loading large cartridges of sensitive explosives is apparent since it is accomplished by dropping the p per wrapped cartridges of explosives into the holes. charge when in place is fired either by an electric blasting cap or by a section of Cordeaurunning the entire length of the hole.

, Various means have been suggested heretofore in an effort to replace the usual relatively sensitive in explosives such as nitroglycerin or nitrostarch dynamites with main explosive charges either of a lower degree of sensitivenessor of a lower velocity.

Favier for example (in U. S. Patent.393,6 34) made use of a high density ammonium nitrate explosive that was characterized by a particularly low degree of sensitiveness. His explosive was in the shape of a hollow cylinder and detonation was brought about by the use of a center core of a more sensitive explosive, such for example as dynamite or gun cotton which is detonated with fulminate. Various disadvantages are however, associated with such an explosive. The use of a hollow cylinder for example, makes it necessary to either ship the assembled explosive with the center core of sensitive primer in place, in which case little advantage can be obtained with respect to insensitiveness to shock, or the hollow cylindrical explosive and priming charge must be '30 shipped separately and assembled at the place of use with resulting inconvenience and danger to the user. 7

Attempts have also been made to utilize black blasting powder in place of nitroglycerin explosives in cases where a high velocity was desirable. Black blasting powder however customarily burns with a velocity of combustion of around 300 meters per second whereas the velocity of detonation of nitroglycerin explosives is usually not 40 below 2000 meters per second? Attempts have been made to increase the velocity of the black powder under such circumstances by the use of a line of high velocity detonating fuse, for example, Cordeau (5000 meters persecond) placed along the entire length of a bore hole filled with the black powder.

has been made by Pratt (U. s. Patent 1,785,529)

who used an explosive assembly comprising e00 unsatisfactory. In the two latter cases'this has Then some explosive i been due to the fact that the velocity of the black powder is really not increased even though its initiation does take place more rapidly throughout the entire bore hole. Furthermore,

5 black powder presents considerable hazard because of its infiammability. In the case of the explosive charges suggested by Favier, the center core priming is not sumcient to impart the desired high velocity to the surrounding explosive. Faviers compositions were, in addition, too insensitive to propagate detonation except as a center core primer was used throughout the entire length of the charge.

Also low strength, low velocity detonating explosives, both of thenitroglycerin and nitrostarch types, have long been made for blasting purposes but have found very limited application in hard for example, less than 2000 meters per second,

and their strength under that of dynamite,

whereas for hard rock quarry blasting the usual practice is to use explosives having 40 strength or above and velocities of over 3000 meters per second.

A further disadvantage common to all of the foregoing explosives lies in the fact that such compositions have but little water resistance. Their use, therefore, has been limited to dry bore holes, a condition which is the exception rather than therule in the well drill" method of quarry blasting.

Heretofore the practicehas been to evalua ex plosives as regards their practical use on the basis of their sensitiveness when initiated unconfined in a diameter of approximately 1 inches by a commercial blasting cap, that is, a No. 6 or No. 8 cap. Those failing to show consistent propagation under such test conditions have generally been considered as too insensitive' to be of practical use.

We have now. discovered that under the confinement normally supplied by the surroundin medium to be blasted many explosive compositions incapable when unconfined of detonation by blasting caps or Cordeau, can be made to detonate and propagate when primed with adequate boosters. Wehave found, however, that for I such insensitive explosives to function even with a booster, the degree of insensitiveness must be regulated between certain limits and that the column or mass of explosive should have across sectional area preferably equal to or greater than that of a two-inch circle or a cross-sectional area of approximately three (3) square inches.

/ Various ingredients of existing explosives may be used in our blasting method and assembly. As examples may be cited inorganic nitrates including those of ammonium, sodium and potassium, and inorganic chlorates and perchlorates such as those of ammonium, sodium and potassium, or equivalent compounds. Since the materials just mentioned are of themselves relatively insensitive, and furthermore since they carry an excessive amount of oxygen, it is necessary to add certain combustible substances which act both as sensitiz'ers and fuels to combine with the excess oxygen present. It has been found that the degree of sensitiveness and the strength of the finished explosive can be satisfactorily regulated by properly choosing the sensitizer and by controlling the amount used. However, for various reasons, both economical and technical, we prefer to use am- 'as just described, so that it is incapable when unconfined of detonation by the strongest commercial blasting cap, and in detonating the main charge by means of one or more booster charges of a more easily deonated explosive. We prefer to have the booster in contact. with the insensitiveexplosive or embedded in a small portion of I the same. Both these methods of priming are possible and in all cases the full efliciency of the explosive is developed if the sensitiveness of the main charge has been properly regulated. Depending upon special conditions, we may either place the booster on top of the charge in the drill hole, at the bottom of thed rill hole or finally at various intermediate points in the column of insensitive explosive. We may also use the center core booster running substantially the full length of the charge. This is not preferred however since our regulated sensitiveness does not require it and furthermore because it is less economical and more hazardous. The position, however, isimmaterial so long as the sensitiveness of the explosive has been properly regulated.

For practical use according to our method of blasting, the main explosive charge must as stated previously, have a degreeof sensitiveness within definite For example, it must be sufficiently insensitive so that it will consistently fail, when unconfined, ,to propagate when initiated bythe strongest commercial deonator in general use, namely a No. 8 cap. As a matter of fact our explosive compositions will fail to detonate with several No. 8 caps fired simultaneously, or with from 5 to 20 grams of TNT primed with a single blasting cap. It is apparent, therefore, that the sensitiveness of the composition is far below that necessary to detonate consistently with a single commercial blasting cap of maximum strength.

On the other hand, the explosive must not be 7 less sensitive than a uniform composition com-. prising 94.5% ammonium nitrate and 5.5% parafiin, these proportions being such that the excess oxygen of the ammonium nitrate is practically sufilcient to combine with thecarbon and hydrogen of the paraifin. As further defining this standardthe ammonium nitrate should be of such fineness that 25% to 40% will pass a mesh screen and finally the density of the finished explosive should not exceed 1.15.

The sensitiveness of the standard mix just described, namely 94.5% ammonium nitrate and 5.5% .parafiin, may also be expressed in terms of a trinitrotoluene primer when using the subsequently described testing method. By a trinitrotoluene primer is meant the quantity of this material at adensity of .95 which is capable of giving a positive result by the test used.

The procedure consists in detonating a single paper-wrapped 45 2 x 8 inch cartridge of the ex-' plosive to be tested after first placing it vertically on a cylindrical lead test block 2% inch in diameter and 4 inches long supported on a substantial steel plate. I

The primer to be used in this method is understood to have the same diameter as that of the explosive under test, namely 4- /2 inches, and consist of trinitrotoluene compressed to a density of 0.95. More specifically the procedure onsists in determining the minimum amount of the said primer when enclosed in a paper wrapper which will cause the insensitive explosive under test to consistently detonate and propagate throughout its entire length of 8 inches. The lead test block is used simply as a convenient means'of indicating whether the detonation has traveled through the 8 inches. Obviously the compression will vary, and will not only depend upon the completeness of the propagation but also on the weight of trinitrotoluene is determined to the nearest inch giving the desired compression.

Experiments have shown that the amount of primer determined by the method just described is greatly in excess of that necessary to produce the required compression particularly when the primer is of a smaller diameter than the main explosive and embedded therein. The use of different length embedded primers of smaller diameter than the main charge however, results, with the standard 8 inch length of main explosive, in a variable distance between the lower end of the primer and the lead block which condition prevents the quantity of the explosive under test from being constant. We therefore prefer to employ a" primer of the same diameter as the main explosive and in this way so standardize the test that the single variable present is the length of primer. The employment of such large primers therefore, is for the sole purpose of insuringa reproduceable and definite method and the amounts as referred to sensitiveness are to be considered as comparative and not in any sense to represent the minimum amount necessary.

The previously described uniform standard composition (94.5 ammonium nitrate 5.5 paramn) when tested at a density of 1.15 by the procedure just described can be madeto detonate and produce the desired compression when primed with 1000 grams of trinitrotoluene.

This same test procedure may be employed when determining the sensitiveness to detonation with a No. 8 cap. or for determining theminimum booster required with the exception that in the case of the cap it is obvious that it would be inserted directly in the explosive. By

a No. 8 cap'we wish to designate one containing sirable that the booster be readily detonated by a commercial blasting cap for example, a No. 6 cap,

by which we wish to designate one containing 'a charge of one gram of mercury fulminate or fulminate composition.

While it is possible to detonate our insensitive explosive by means of a booster of relatively smalldiameter embedded in the explosive, ;or bya booster of appreciably smaller diameter than the in charge, said booster not being enclosed ereby but in direct contact with the main explosive, we prefer to bring about detonation by the use of a primer butted against and of substantially the same diameter as the main column of explosive. As previously stated, the booster charge may be placedat either or both ends of the main explosive column. It may also be located at one or more intermediate points in the column depending upon special conditions.

Our invention renders available for blasting many compositions fundamentally more economical than those heretofore used and at the same time makes possible a great increase in safety. While our-invention is intended to include the use with the booster of any explosive coming within the limits of sensitiveness already defined, we find ammonium nitrate particularly'well adapted for use in explosive compositions-capable .of use in our preferred method of blasting.

The ease of detonation of ammonium nitrate can be varied withinwide limits depending on the nature of sensitizer or carbon carrier added to it. Variation in density of the finished explosive and also in the fine ass of the nitrate of ammonia produces marked c anges in the sensitiveness. For any given composition the density must not be too high or else the explosive will be too insensitive. Likewise for any given fineness of nitrate of ammonia 'there are certain compositions and densities which favor the proper sensitiveness.

v A mixture of 94.5 per cent. ammonium nitrate and 5.5 per cent. para 7 has already been cited as representing an explosive approximating the upper limit of sensitiveness satisfactoryfor our 1 method of blasting, provided the ammonium nitrate' has a certain fineness and the finished explosive a density not exceeding 1.15. This combination can be rendered well suited for use in our method of blasting by a number of means. For

example, by-materially increasing the fineness of;

thenitrate of ammonia or by lowering the density to a point approximating 1.0 the sensitiveness of this mixture is improved. Likewise by replacing either a 'porton or all of the paramn by more efiicient sensitizers, such as for example nitro aromatic compounds, the above composition can be rendered well adapted for use in our combination method of blasting, provided of course due attention is given to maintaining a reasonable oxygen balance.

, Ammonium nitrate explosives are, however, not

' suitable for use in bore holes where water is present except as they are properly protected from its solvent action. In the case of dry bore holes unprotected ammonium nitrate explosives may be used in our blasting assembly. We prefer however, to enclose themain explosive charge in waterproof containers made preferably of metal. In the use of explosives in well drill holes, water is very frequently present, and in the case of deep holes containing considerablev water the pressure of this water makes it necessary that the explosive be completely protected. A rigid container, such as can be'madc from sheet metal has other advantages such as keeping out atmospheric moisture and preventing a change in the density when loaded in deep' holes which change can be brought about normally by excessive tamping or by dropping the charges for considerable distances. In

other words, a tightly sealed metal container' thetime of its manufacture. Furthermore, the

' metal containers without any question as to hazard, which is not the case with the dynamites heretofore used in mines and quarries.

As'an example of the procedure involved our method of blasting we may cite the following. An ammonium .nitrate explosive so regulated as to sensitiveness as to fall within the previously given limits is cartridged in cylindrical water tight containers, for example, 4 x 16' inches at a density consistent with both sensi- I tiveness and strength. These containers may then be loaded one on top of the other in the proper amount in a well drill quarry hole of 100-foot depth filled with water. The main charge can then be detonated with full efficiency by the use of one 4 x 16 inch paper cartridge of 60% gelatin dynamite placed directly on top of the last container of insensitive explosive. The gelatin may in turn be detonated either by means of an electric blasting cap or by Cordeau fuse.

Having described in detail our invention, many modifications of which are .possible we wish to be limited only by the following claims. It is understood that the degree of sensitiveness in the said claims is that determined by the method of testing herein described.

We claim:

1. A blasting assembly comprising a cap-sensitive booster charge, an initiator for the booster, and a detonating explosive consisting of at least one charge having a length substantially greater than the booster and capable of complete detonation when once initiated by said booster, and having a degree of sensitiveness such that its initiation requires a booster charge in addition to a blasting cap, but having an insensitiveness not greater than that of a composition at a density of 1.15 comprising 94.5% ammonium nitrate, of such fineness that to will pass a 100-mesh screen, and 5.5% paramn.

2. Ablasting assembly comprising a cap-sensi tive booster charge, an initiator for the booster, and a detonating explosive charge having a length substantially greater than the booster and capable of complete detonation when once initiated by said booster, and having a degree of insensitiveness, when tested unconfined, such that its complete detonation requires, in addition to a blasting cap, a booster charge not to exceed 1000 grams of TNT at a density of 0.95.

3. A blasting assembly-comprising a cap-sensitive booster charge, an initiator for the booster, and a charge of an ammonium nitrate detonating explosive having a length'substantially greater than the booster and capable of complete detonation when once initiated by said booster, and having a degree of insensitiveness, when tested unconfined, such that its complete detonation requires, in addition to a blasting cap, a booster charge not to exceed 1000 grams of TNT at a density of 0.95. i l

4. A blasting assembly comprising a cap-sensitive booster charge, an initiator for the booster, and a plurality of charges of a detonatingexplosive capable of complete detonation when once initiated by'sa'd booster, and comprised of ammonium nitrate, the combined length of said charges being substantially greater than the booster, said explosive having a degree of insensitiveness, when tested unconfined, such that its complete detonation requires, in addition to a blasting cap, a booster charge not to exceed 1000 grams of TNT at a density of 0.95, said capsensitive booster one ofthe plurality of explosive charges.

,5. A blasting assembly. comprising a cap-sensitive booster charge, aninitiator for the booster, and a detonating explosive capable of complete detonation when once initiated by said booster, and comprised of ammonium nitrate enclosed in a waterproof container, said charge having a cross-sectional area of not less than 3 inches and a length substantially greater than the booster,

'said explosive having a degree of insensitiveness,

when tested unconfined, such that its complete detonation requires, in addition to a blasting cap, a booster charge not to exceed 1000 grams of TNT at a density of 0.95.

6. A blasting assembly comprising a cap-sensitive booster charge, an initiator for the booster, and aplurality of charges'of a detonating explosive capable of complete detonation when once initiated by said booster, and comprising ammonium nitrate in a waterproof container, said charges having a length substantially greater than the booster, said explosive having a degree of insensitiveness, when tested unconfined, such that its complete detonation requires, in addition to a blasting cap, a booster charge not to exceed 1000 grams of TNT at a density of 0.95, said cap-sensitive booster charge being in contact with one of the plurality of explosive charges.

7. A blasting assembly comprising a cap-sensitive booster charge, an initiator for the booster and a detonating ammonium nitrate explosive capable of complete detonation when once initiated by said booster, and having a diameter not less than two inches and a length substantially greater than the booster and having a degree of insensitiveness, when tested unconfined; such that its complete detonation requires, in addition to a blasting cap, a booster charge not to exceed 1000 grams of TNT at' a density of 0.95.

8. A blasting assembly comprising a cap-sensitive booster charge, an initiator for the booster, and a detonating explosive charge substantially greater inlength than the booster and capable of complete detonation when once initiated by said booster, and comprised of ammonium nitrate, enclosed in a metallic water-- proof container, to prevent a change in density of the explosive, and having a diameter of not less than two inches, said explosive having a degree of insensitiveness, when tested unconfined, such that its complete detonation requires, in addition to a blasting cap, a booster charge not to exceed 1000 grams of TNT at a density of 0.95.

9. A blasting assembly comprising a cap-sensitive booster charge, an initiator for the booster, and a detonating ammonium nitrate explosive capable of complete detonation when once initiated by said booster, and having a diameter of not less than two inches, and a length substantially greater than the booster, said explosive having a degree of insensitiveness, when tested unconfined, such that complete detonation with the propagation of the explosive wave throughout the entire charge requires, in addition to a blasting cap, a booster charge not to exceed 1000 grams of TNT at a density of 0.95.

10. The method of blasting with a booster which comprises loading a blasting cavity with an explosive charge whose length is substantially greater than the booster, detonating a limited amount of the explosive by means of a booster and propagating the detonation throughout the charge being in contact with 94.5% ammonium nitrate of such a fineness that.

.25% to 40% will pass a 100-mesh screen and 5.5% paraflin at a density of 1.15.

11. The method -of blasting with a booster which comprises loading a blasting cavity with a plurality of explosive charges, causing the detonation of one of the charges only, by priming said charge with a booster and propagating-the I detonation throughout the plurality of charges by the inherent characteristics of the explosive,

said explosive-"havingv a regulated sensitiveness incapable, when unconfined, of detonation by means oi a-No. 8 can but having a sensitiveness not less than that of a composition comprising 94.5% ammonium nitrate of such fineness that .2s% to 40% will pass a IOU-mesh screen and 5.5% parafiin at a density of 1.15.

12. The method of blasting. with a booster which comprises loading the blasting cavity with an explosive charge substantially greater in length than the booster, detonating a limited means of a booster and propagating the detonation throughout the length and breadth of the charge unaided except bymeans of the limited amount of the charge detonated by 'the booster, said charge having a regulated sensitiveness so that it is incapable, when unconfined, of detonation by means of a No. 8 cap but having a sensitiveness such that it can, when unconfined, be detonated by means 1000 grams of trinitrotoluene at a density oi 0.95.

13. The. method of blasting with a plurality of boosters which comprises loading a blasting cavity with an' explosive charge having an aggregate length substantiallyv greater than the length of the booster, detonating a limited amount of the explosive by means or separated booster charges and propagating the detonation through- .out the length and breadth ofthe charge unthat it is incapable, when unconfined, of deto-,

nation by means of a; No. 8 cap but having a sensitiveness such that it can, when unconfined, be detonated by means of 1000 grams of trinitrotoluene at a density of 0.95. y

. 14. The method of blasting with a booster which comprises loadingthe blasting cavity with aplurality of explosive charges, and causing the plurality of charges to detonate and propagate only by priming one of said charges with a booster, said charges having a regulated sensitiveness incapable, when unconfined, of detonation by means of .a No. 8 cap but having a sensitiveness such that it can, when unconfined, be detonated by means of 1000 grams of trinitr otoluene at a density of 0195.

15. The methodof blasting with a booster which comprises loading the blasting cavity with a plurality of explosive charges, and causing the plurality of charges to detonate and propagate by a plurality or booster charges, said-charges having a length substantially greater than the length of the booster and being capable of complete detonation when once initiated by said booster, and having a regulated sensitiveness incapable, when unconfined, of detonation by means of a No; 8 cap but having a sensitiveness such that theycan, when unconfined, be detonated by means of 1000 grams of trinitrotoluene at a density of 0.95.

16. The method of blasting with a booster which comprises loading a blasting cavity with an am monium nitrate detonating explosive charge having a length substantially greater thanfthe booster, detonating a limited amount of the explosive by means of a; booster charge and propagating the detonation throughout the length and breadth of the main charge unaided except by means of the limited amount of the charge detonated by the booster, said detonating explosive having a regulated sensitiveness so that it is incapable, when unconfined, of detonation by means of a No. 8 cap but having a sensitiveness such that it can, when unconfined, be detonated by means of 1000 grams of trinitrotoluene at a density oi. 0.95.

17. The method of blasting with a multiplicity of boosters which comprises loading a blasting cavity with an ammonium nitrate detonating explosive charge, having an aggregate length substantially-greater than the length of the boostby the plurality of separated booster charges and propagating the detonation throughout the length and breadth of the charge unaided except by means of the limited amount of the charge detonated by the boosters, said detonating explosive having a regulated sensitiveness so that it is incapable, when unconfined, detonation by means of a No. 8 cap but having a sensitiveness such that it can, when unconfined, be detonated by means 011000 grams of trinitrotoluene at a density of 0.95;

18. The method of blasting with a booster which comprises loading a blasting cavity with a plurality of charges of an ammonium nitrate detonating explosive, causing the plurality of charges to detonate and propagate only by priming one of said charges with a booster charge capable of detonation by a No. 6 cap, said explosive having a regulated sensitiveness incapable, when unconfined, or detonation by means of a No. 8 cap, but having a sensitiveness'such that it can, when unconfined, be detonated by means of 1000 grams of trinitrotoluene at a density of 0.95.

19. The method of blasting with a booster which comprises loading a blasting cavity with means of the limited amount of the charge detonated by the booster, said explosive having a regulated sensitiveness so that it is incapable, when unconfined, of detonation by means of a No. 8 cap but having a sensitiveness not less than that of a composition comprising 94.5% ammonium nitrate of such fineness that 25% to 40% will pass a IOU-mesh screen and 5.5% p'araflin at a density of 1.15.

WILLIAM E. KIRST. JOHN w. McCOY. CLIFFORD A. WOODBURY. 

